The use of unmanned aerial vehicles (“UAV,” or drones) such as airplanes or helicopters having one or more propellers in a variety of applications (e.g., surveillance, delivery, monitoring, law enforcement, security, mapping, or the like) is increasingly common. Such vehicles may include fixed-wing aircraft, or rotary wing aircraft or other vertical take-off and landing (or VTOL) aircraft having one or more propellers. In most unmanned aerial vehicles, each of the propellers is powered by one or more rotating motors or other prime movers. Additionally, most unmanned aerial vehicles are outfitted with inertial measurement units that measure linear and/or angular motion of the unmanned aerial vehicles, thereby enabling the unmanned aerial vehicle to calculate adjustments that may be necessary in order to maintain the unmanned aerial vehicle at a desired altitude, on a desired course or in a desired angular orientation.
Accurately determining moment of inertia values for an aerial vehicle can provide improved flight control capabilities. Unlike a solid body having a uniform mass distribution, an aerial vehicle is typically formed from a variety of different materials, and may feature asymmetric, irregular or uneven distributions. Therefore, determining moments of inertia of an aerial vehicle is typically a more challenging task than determining moments of inertia of a solid body having a uniform mass distribution, and commonly requires conducting one or more experiments, rather than calculating one or more values according to well-established equations.
Currently, one process for experimentally determining a moment of inertia of an object is a bifilar pendulum technique, or a bifilar suspension technique. In a typical bifilar pendulum technique, an object is suspended by a pair of parallel connectors, or filars, having substantially equal lengths. The object is then caused to oscillate about a vertical axis, e.g., as a torsional pendulum. A moment of inertia of the object about the vertical axis may be calculated as a function of lengths of the filars, a period of oscillation of the object, and a mass of the object. The process may be repeated any number of times, with the object in various orientations, in order to calculate values of moments of inertia about vertical axes with the object in the respective orientations.
When calculating moment of inertia tensors of aerial vehicles, typical bifilar pendulum techniques are plagued by a number of limitations. First, in order to determine moments of inertia about principal axes of an aerial vehicle, viz., a normal axis (or yaw axis), a lateral axis (or pitch axis), and a longitudinal axis (or roll axis) of the aerial vehicle, the aerial vehicle must be properly suspended in specific orientations such that the principal axes are respectively aligned along a vertical axis. In the event that the aerial vehicle is not properly oriented during a bifilar pendulum technique, e.g., with one of its axes aligned along the vertical axis about which the aerial vehicle oscillates, a moment of inertia calculated following the bifilar pendulum technique will not accurately reflect the true moment of inertia about that axis. Moreover, during a typical bifilar pendulum technique, a period of oscillation is typically measured by hand, e.g., using a stopwatch or other timing device. Inaccuracies in the timing of a period necessarily impact the accuracy of a moment of inertia calculated thereby.